The present invention relates to a vehicle damping sheet applicable to floors, dash panels, etc. of automobiles and, more in particular, it relates to a vehicle damping sheet of light-weight, having high damping effect.
As is well known, damping material has been used generally to various application-uses for the protection of precision equipments against vibrations, damping of vibrations of engines in vehicles, etc. and damping of vibrations of floors and walls in buildings or houses.
As damping sheets used for vehicle damping material, there have been proposed damping sheets comprising blends of inorganic fillers such as carbonate, mica and clay, and as a binder, bituminous material such as asphalt [refer to Japanese Patent Application Laid Open (KOKAI) No. 63-156859 (1988) and Japanese Patent Publication No. 52-50522 (1977)] as well as noise-insulation sheets comprising blends of a thermoplastic resin such as vinyl chloride resin as a binder, iron or iron oxide, and silicon oxide [refer to Japanese Patent Application Laid Open (KOKAI) No. 61-57632 (1986)]. There are further proposed damping sheets comprising blends of an epoxy resin as the binder, iron oxide or iron oxide, and mice [refer to Japanese Patent Application Laid Open (KOKAI) No. 60-215013 (1985), No. 60-215014 (1985), No. 61-103977 (1985), No. 61-151227 (1986), and No. 63-178037 (1988)].
In particular, Japanese Patent Application Laid Open (KOKAI) No. 60-215013 (1985) discloses a damping material comprising a composition composed of 100 parts by weight of an epoxy resin and a curing agent; 0.1 to 70 parts by weight of a different kind polymeric material such as nitrile rubber, butadiene rubber, polyethylene, polypropylene and modified polyethylene; 40 to 900 parts by weight of a granular iron oxide such as Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 ; 0.5 to 50 parts by weight of a fibrous material such as asbesto and polyamide; and 0.5 to 50 parts by weight of a flaky filler such as mica, graphite flake, alumina flake, etc.
Further, Japanese Patent Application Laid Open (KOKAI) No 61-151227 (1986) discloses a damping material comprising a composition composed of 100 parts by weight of an epoxy resin and a curing agent; 50 to 500 parts by weight of a flaky filler such as mica, alumina flake and iron oxide flake; 0.5 to 200 parts by weight of a granular filler such as calcium carbonate, talc and ferrite; 0.5 to 100 parts by weight of a fibrous material such as asbesto, polyamide fiber and carbon fiber; and 80 to 300 parts by weight of a plasticizer.
Generally, the damping effect of a damping sheet has a close relationship with the loss of viscosity of the damping sheet and in order to increase the damping effect, there has been adopted a method of controlling the composition of the damping sheet so as to increase the viscosity loss, or increasing the thickness of the damping sheet, etc.
In addition, the damping effect can also be improved by increasing the weight of the damping sheet and, in this case, there has been adopted a method of adding a great amount of a high density filler.
That is, for improving the damping effect, the conventional damping sheets has usually been manufactured by controlling the composition so as to increase the viscosity loss, increasing the thickness of the damping sheet or incorporating a great amount of various fillers to increase the weight thereof.
However, when a damping sheet with increased thickness and weight is used for vehicles such as automobiles, it increases the weight of the vehicle and is not suitable to vehicles for which light-weight thereof is demanded. In the case of manufacturing a damping sheet incorporating a great amount of filler, since the damping effect can be improved, particularly, by increasing the content of the filler, the aimed damping effect can be obtained even when the thickness of the sheet is reduced as compared with the case of containing a less amount of filler. However, as the result, various problems such as worsening of the physical property of the damping sheet and the fusing property, and further, lowering in the productivity due to the increased mechanical abrasion upon manufacturing the sheet, occur.
For obtaining a vehicle damping sheet as the vehicle damping material of light weight and having a high damping effect within a wide temperature range, the present inventors have made a study on a damping effect of the damping sheet prepared by molding a blend mixture comprising a filler and a binder into a sheet, as well as the relationship between the filler and the binder as the starting materials, and as a result, it has been found that a vehicle damping sheet of light-weight and having high damping effect within a wide temperature range can be obtained by:
selecting a combination of mica and iron oxides particle as one of a filler,
selecting, as a binder those (a) containing a bituminous material, or (b) containing an ethylene-vinyl acetate copolymer, and
adjusting the mixing ratio of each of mica and iron oxide particles to not less than 5 parts by weight based on 100 parts by weight of the binder, the mixing ratio of the filler to not less than 30 parts by weight based on 100 parts by weight of the binder and the amount of the iron oxide particles in the blend-mixture to 2 to 40% by weight. Based on the finding, the present invention has been attained.